Transfer switch for tap-changing regulating transformers including lost motion interconnection driving mechanism

ABSTRACT

In a polyphase transfer switch for tap-changing regulating transformers the cooperating fixed and movable contacts of each phase are arranged to form a pattern in the shape of a sector of a circle. The movable current-carrying contacts are hingedly supported by the movable main contacts. Due to the presence of a lost motion connection the current-carrying contacts are separated prior to separation of the main contacts, and on account of this lost motion connection cooperating current carrying contacts are brought into engagement only after the main contacts are brought into engagement.

United States Patent Bleibtreu 1 June 20, 1972 54] TRANSFER SWITCH FOR TAP- 3,250,865 5/1966 Bleibtreu et al. ..200/11 TC CHANGING REGULATING FOREIGN PATENTS 0R APPLICATIONS TRANSFORMERS INCLUDING LOST MOTION INTERCONNECTION gammy ermany DRIVING MECHANISM 239,929 9/1964 Austria [7 2] inventor: Alexander Blelbtreu, Regensburg, Germany [73] Assignee: Masehinenlabrik Relnhausen Gebruder Prmmry Examiner-l Scheubeck K.G., Regensburg, Germany A!t0rney-Erwin Salzer [22] Filed: Dec. 7, 1970 l 57] ABSTRACT [2]] Appl' 95428 In a polyphase transfer switch for tap-changing regulating transformers the cooperating fixed and movable contacts of [30] Foreign Application Priority Data each phase are arranged to form a pattern in the shape of a Dec 1 6 I969 Germany P 19 62 958 4 sector of a circle. The movable current'carrying contacts are hingedly supported by the movable main contacts. Due to the 521 user. ..20o/11Tc, 200/153 v Presence of a lost Cmmfion the current-carrying [51] Int. Cl ..H0lh 21/38, l-lOlh 21/20 contacts are Separated Prior Separation of the main [58] Field of Search "200/1 1 TC, 153 V tacis, and On account f hi 10 1 motion connection cooperating current carrying contacts are brought into engagement [56] References Cited only after the main contacts are brought into engagement.

UNITED STATES PATENTS 6 Claim, 4 Drawing Figures 3,238,318 3/1966 Bleibtreu et al. ..200/ll TC PATiNTEnJunzo um I 3,671,687

AvrzwroP M W W 2%- WMMM 3M TRANSFER SWITCH FOR TAP-CHANGING REGULATING TRANSFORMERS INCLUDING LOST MOTION INTERCONNECTION DRIVING MECHANISM BACKGROUND OF INVENTION Tap-changing regulating transformers include three basic elements, Le. a tapped transformer winding, a selector switch for selecting any desired tap on said winding, and a transfer switch for connecting a load to the particular tap selected by the selector switch. This invention relates to improved transfer switches, and more particularly to transfer switches of the type known as Jansen type transfer switches.

Regulating transformers and Jansen type transfer switches are disclosed in detail in the patents which are identified below:

US. Pat. Nos. 3,176,089 to A. Bleibtreu et al., Mar. 30, 1965 for Load Tap Changers for Transformer; 3,218,400 to A. Bleibtreu, Nov. 16, 1965 for Transfer Switch For Tap- Changing Regulating Transformers Having Squirrel-Cage- Shaped Support For The Fixed Contacts Thereof; and 3,238,320 to A. Bleibtreu, Mar. 1, 1966 for Transfer Switch For Tap Changers For Regulating Transformers Including A Cylindrical Insulating Housing, A Squirrel-Cage Contact-Supporting Structure And Contact Bridges lnsulatingly Supported By Contact Bridge Carriers.

FIG. 4 of the first mentioned patent shows a circuit diagram including a tapped transformer winding, a selector switch and a transfer switch and the coaction of these three elements is described in the context of FIG. 4. The last mentioned patent shows in FIGS. 1,2 and 3 thereof various circuit connections of transfer switches which are described in detail in the context of FIGS. 1-3. FIG. 9 of U.S. Pat. No. 3,238,320 shows and its context describes the operation of the main contacts and the auxiliary contacts in a transfer switch of the Jansen type, and FIG. 12 of that patent shows in what fashion current-carrying contacts may be added to the main contacts and the auxiliary contacts in a transfer switch of the Jansen type. The con text of FIG. 12 describes in detail the function of the current carrying contacts, and the way in which such contacts may be operated.

The function of current-carrying contacts is to shunt a pair of cooperating main contacts during periods of time when no tap changes are performed, and thus to relieve the pair of cooperating main contacts largely of their current-carrying duty. In conventional designs such as that shown in the above referred-to U.S. Pat. No. 3,23 8,320 the gaps formed between the separated cooperating current-carrying contacts are relatively small, and this is a major limitation of these designs. To avoid this limitation of prior art designs relatively complex operating mechanisms for the movable current-carrying'contacts had to be evolved.

The present invention refers to a transfer switch wherein large gaps between the separated current-carrying contacts can be achieved by extremely simple and inexpensive operating means for the latter.

The operation of current-carrying contacts must be independent of the degree of erosion of the main contacts. This requirement could not be fulfilled up to this time unless the movable current-carrying contacts were provided with complex compensating mechanisms for the erosion to which the main contacts are subjected. Transfer switches embodying this invention achieve large gaps between the parting current-carrying contacts at high separation velocities, irrespective of the degree of erosion of the current-carrying contacts, by operating means which are utterly simple and very inexpensive.

SUMMARY OF INVENTION A transfer switch for tap-changing regulating transformers embodying this invention includes a substantially cylindrical contact support of insulating material. A plurality of fixed contacts supported by said contact support are arranged in a circular pattern. Said plurality of fixed contacts includes fixed main contacts, fixed auxiliary contacts arranged between said fixed main contacts, and fixed current-carrying contacts each arranged adjacentone of said fixed main contacts on the side thereof opposite to one of said fixed auxiliary contacts. The transfer switch is further provided with aplurality of movable contacts each arranged to selectively engage one of said plurality of fixed contacts, and to be-separated from said one of said plurality of fixed contacts. The aforementioned plurality of movable contacts includes movable main contacts each arranged to cooperate with one of said fixed main contacts, movable auxiliary contacts each arranged to cooperate with one of said fixed auxiliary contacts, and movable current-carrying contacts each arranged to cooperate with one of said fixed current-carrying contacts. Each of said movable currentcarrying contacts has a lateral projection extending toward one of the movable main contacts immediately adjacent thereto. A. drive shaft selectively pivotable in opposite directions for operating said plurality of movable contacts is arranged along the axis of said contact support. Transfer switches embodying this invention further include a plurality of contact-operating links. Each of these contact-operating links has a radially inner pivot pin jointly pivotable with said drive shaft, and a radially outer pivot pinaffixed to one of said plurality of movable contacts. The radially outer pivot pin affixed to each of said movable main contacts projects through said lateral projection of one of said movable current-carrying contacts and hingedly supports said one of said movable current-carrying contacts on said one of said movable main contacts.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a vertical section of a transfer switch embodying the present invention taken along 1-1 of FIG. 3 with portions of the contact-operating links broken away in order not to encumber FIG. 1;

FIG. 2 is avertical section of the structure of FIG. 1 taken along "-11 of FIG. 1;

FIG. 3 is a top plan view of the structure of FIGS. 1 and 2; and

FIG. 4 shows a-portion of the structure of FIG. 3 in the same fashion as FIG. 3 but in another operating position.

All figures refer to a polyphase or three phase transfer switch, but only the parts pertaining to one phase of the switch have been fully shown since this makes the arrangement of the parts of the other two phases of the switch fully apparent.

DESCRIPTION OF PREFERRED EMBODIMENT The transfer switch includes a substantially cylindrical contact support 10 of insulating material supporting a plurality of fixed contacts 11,12,13,l4 arranged in a circular pattern, or in the form of a sectorof a circle. in order to establish double breaks contacts '1 1,12,13,14 are arranged at two different levels, and form two circular coaxial patterns. The transfer switch further includes a plurality of movable contacts 21,22,23 and 34. Fixed contacts 11,12 are main contacts and movable contacts 21,22 are cooperating main contacts each arranged to selectively engage one of fixed rnain contacts 11,12 and to beseparated from said oneof fixed main contacts 11,12. Fixed contacts 13 areauxiliary contacts and are arrangedbetween fixed main contacts 11,12. Fixed auxiliary contacts 13 cooperate with movable auxiliary contacts 23,

each of the latter being arrangedto selectively engage one of the fixed auxiliary contacts 13, and to be separated from said one of said fixed auxiliary contacts 13. Fixed contacts 14 are current-carrying contacts. Each fixed current-carrying contact 14 is arranged adjacent one fixed main contact 11, 12 on the side thereof opposite to onefixed auxiliary contact 13 immediately adjacent thereto. Fixed current-carrying contacts 14 cooperate with movable current-carrying contacts 34. Each of'the latter is arranged to selectively engage one of the fixed current-carrying contacts 14, and to be separated from said one of the fixed current-carrying contacts 14.

The function of a cooperating pair of current-carrying contacts is to carry current after engagement of a cooperating pair of main contacts arranged in the same current path, and thus to relieve the pair of main contacts of their current-carrying duty during the time of engagement thereof. To this end the low resistance current-carrying contacts shunt the high resistance main contacts which are arranged in the same current path. Since current-carrying contacts are designed to, and capable of, carrying currents, but not capable of breaking currents, or to withstand arcing, the current-carrying contacts must be separated before the main contacts arranged in the same current path are separated. How this is achieved in the instant case will be shown below in detail.

The movable main contacts 21,22 and the movable contacts 23 have upper and lower projections engaging radially extending grooves 24 in a pair of end plates 25 arranged at right angles to the axis of cylindrical contact support 10. Thus each movable main contact 21,22 and each movable auxiliary contact 23 is guided along a straight path or trajectory, defined by a pair of radially extending grooves 24 in end plates 25. The fixed main contacts 11,12 and the fixed auxiliary contacts 13 are aupported on support by contact supporting studs which project transversely through support 10 as clearly shown in FIGS. 1,3 and 4. Helical spring means are interposed between each fixed contact 11,12,l3,14 and support 10 to cushion contacts 11,12,13,14. Each of the movable currentcarrying contacts 34 is provided with a lateral projection 35 extending toward the movable main contact 21 immediately adjacent thereto.

Reference numeral 26 has been applied to indicate a plurality of links for operating the movable main contacts 21,22 and for operating the movable auxiliary contacts 23, and reference numeral 38 has been applied to indicate a pair of links for operating movable current-carrying contacts 34. Each movable main contact 21, 22 and each movable auxiliary contact 23 is provided with a pair of operating links 26 which are arranged at different levels. In FIG. 1 the two level arrangement of operating links 26 has been clearly shown. In that figure the radially outer ends of links 26 are shown as being broken away. FIG. 2 shows in part a pair of superimposed links 26 for operating movable main contact 21 which cooperates with fixed main contact 11.

A Y-shaped drive shaft 28 selectively pivotable in opposite directions is arranged along the axis of contact support 10.

Drive shaft 28 is provided with a pair of axially spaced hub members or contact-operating members 27 which pivot in clockwise and counter-clockwise direction jointly with drive shaft 28. Each contact operating link 26 is provided with a radially inner pivot pin 29 supported and operated by one of members 27, and hence jointly movable with shaft 28. As shown in FIGS. 3 and 4 each contact-operating member 27 is provided with three radially extending slots 30 which are angularly displaced 120 degrees. Each of slots 30 is a means for operating the movable main contacts 21,22 and the movable 5 auxiliary contacts 23 pertaining to one phase of a three phase circuit. All upper level links 26 pertaining to one phase have a common pivot pin 29 arranged in the radial slot 30 of the upper level contact-operating member 27, and all lower level links 26 pertaining to one phase have a common pivot pin 29 arranged in a radial slot 30 of the lower level contact-operat ing member 27. This is clearly shown in FIG. 1. Each slot 30 receives in addition to a pivot pin 29 a helical spring 31 biasing the adjacent pivot pin radially outwardly away from the axis of contact support 10. Each contact-operating link 26 is provided with a radially outer pivot pin 36 affixed to a movable main contact 21,22, or to a movable auxiliary contact 23, respectively.

Reference character 40 has been applied to indicate a third hub-member, or contact-operating member, fixedly mounted on Y-shaped drive shaft 28 between hub-members of contact operating members 27 and jointly pivotable with shaft 28. Hub member 40 is provided with bearings for pivot pins which are arranged in the general vertical planes defined by slots 30 in hub members 27, but which are arranged more remotely from the axis of shaft 28 than slots 30, or radially outwardly from slots 30. Each movable current-carrying contact 34 is operated by a link 38 having a radially outer pivot pin 37 affixed to one of movable current-carrying contacts 34 and haw ing a radially inner pivot pin 39 arranged in the pin bearing formed by contact-operating member 40. Pivot pin 39 is common to the operating links 38 of both movable current-carrying contacts 34. Since the radial spacing of pivot pin 39 from the axis of shaft 28 exceeds the radial spacing of pivot pins 29 from the axis of shaft 28, the velocity of pivot pin 39 exceeds the velocity of pivot pins 29 when shaft 28 is being pivoted in either direction by motor means not shown. The radially outer pivot pins 37 of links 38 are affixed to, or supported by, movable current-carrying contacts 34. Movable current-carrying contacts 34 have contact surfaces which are substantially circular in cross-section, i.e., these contact surfaces are substantially cylindrical. The contact surfaces of movable currentcarrying contacts 34 are arranged in coaxial relation to the radially outer pivot pins 37 of contact-operating links 38. The contact surfaces of the fixed current-carrying contacts 14 are planar. The lateral projections 35 of movable current-carrying contacts are pivotally connected to movable main contacts 21, 22 by means of pivot pins 36 extending across projections 35 as well as across the radially outer ends of operating links 26 for movable main contacts 21,22.

The difference of the radii of rotation of pivot pins 29 and 39 and the freedom of motion of pins 29 against the bias of springs 31 is responsible for the fact that movable current-carrying contacts 34 part from fixed current-carrying contacts 14 before the movable main contacts 21,22 part from the fixed main contacts 11,12, and that the movable current-carrying contacts 34 engage the fixed current-carrying contacts 14 only after the movable main contacts 21,22 have engaged their cooperating fixed main contacts 11,12. I

The operation of a transfer switch embodying this invention shown in FIGS. 1-4 is as follows:

Considering FIG. 3 and assuming that Y-shaped drive shaft 28 is pivoted in clockwise direction, this causes a corresponding pivotal motion of part 40, and of the two links 38 for operating movable current-carrying contacts 34. As a result, movable current-carrying contacts 34 are pivoted about pin 36 relative to movable main contacts 21,22. To be more specific, the upper movable current-carrying contact (FIG. 3) is separated from fixed current-carrying contact 14 before occurrence of any relative movement between main contacts 11, 21. During the period of time required for parting of currentcarrying contacts 14,34 main contacts 11,21 remain in engagement on account of the fact that pins 29 move during this period of time relative to parts 27 from their radially outer position in slots 30 to their radially inner position in slots 30 so that no radial inward motion is imparted to pins 29 and to operating links 26 of movable main contacts 21,22. In other words, the pin-receiving slots 30 operate as a lost motion connection delaying the separation of contacts 1 1,21 following initiation of the pivotal motion of drive shaft 28. The main contacts 11,21 remain closed until after engagement of the first pair of cooperating auxiliary contacts 13,23 immediately adjacent to cooperating main contacts 11,21. While main contacts 11,21 are separated from each other the gap between current-carrying contacts 14,34 grows at a faster rate than the gap between main contacts 11,21. While FIG. 3 shows one limit position of contacts 34,21, FIG. 4 shows their other limit position in which contact 34 is entirely separated from contact 14 and contact 21 is fully separated from contact 11. It is apparent from FIG. 4 that the length of the ultimate gap between current-carrying contacts 14,34 by far exceeds the length of the ultimate gap between main contacts 11,21. As the pivotal motion'of drive shaft 28 continues the movable contacts of the structure are operated in their required conventional sequence at the end of which movable main contact 22 is being moved radially inwardly into engagement with fixed main contact 12, whereupon movable current-carrying contact 34 pivotally affixed to movable main contact 22 is pivoted about pin 36 into full engagement with fixed lower currentcarrying contact 14 of FIG. 3.

The main contacts 11,21 and 12, 22 are arcing contacts and are, therefore, subject to contact erosion. Their erosion has,however, no effect upon the initial movement of separation of current-carrying contacts 34 from current-carrying contacts 14 because the erosion of contacts l1,l2,21,22 has no effect on the spacing between the axis of shaft 28 and the point of engagement of current-carrying contacts 14,34.

When the transfer switch has been pivoted from its limit position shown in FIG. 3 to its opposite limit position it may be returned to its original limit position by pivoting drive shaft 28 in counter-clockwise direction, as seen in FIG. 3. This causes initially a separation of the movable current-carrying contact 34 pivotally connected to the movable main contact 22 from its cooperating current-carrying contact 14. Thereafter main contact 22 parts from its cooperating fixed main contact 12, while the separation of the current-carrying contact 34 which is hinged to it from its cooperating fixed current-carrying contact l4 continues.

I claim as my invention:

l. A transfer switch for tap-changing regulating transformers including a. a substantially cylindrical contact support of insulating material;

b. a plurality of pairs of fixed contacts supported by said contact support and arranged in a circular pattern, the constituent contacts of each of said plurality of pairs of contacts being spaced in a direction longitudinally of the axis of said contact support, said plurality of pairs of fixed contacts including pairs of fixed main contacts, pairs of fixed auxiliary contacts arranged between said pairs of fixed main contacts, and pairs of fixed current-carrying contacts each arranged adjacent one of said pairs of fixed main contacts on the side thereof opposite to one pair of said pairs of fixed auxiliary contacts;

c. a plurality of movable contact bridges each arranged to selectively engage one of said plurality of pairs of fixed contacts and to be separated from said one of said plurality of pairs of fixed contacts, said plurality of contact bridges including main contact bridges each arranged to cooperate with one pair of said pairs of fixed main contacts, auxiliary contact bridges each arranged to cooperate with one pair of said pairs of fixed auxiliary contacts, and current-carrying contact bridges each arranged to cooperate with one pair of said pairs of fixed current-carrying contacts, each of said current-carrying contact bridges having a pair of lateral projections spaced in a direction longitudinally of said axis of said contact support and extending toward one of said main contact bridges immediately adjacent thereto;

(1. a drive shaft selectively pivotable in opposite directions for operating said plurality of contact bridges arranged along the axis of said contact support; and

e. a plurality of contact-operating link means each having a radially inner pivot pin jointly pivotable with said drive shaft and a radially outer pivot pin affixed to one of said plurality of contact bridges, and said radially outer pivot pin afiixed to each of said main contact bridges projecting through said pair of lateral projections of one of said current-carrying contact bridges and hingedly supporting said one of said current-carrying contact bridges on said one of said main contact bridges.

2. A transfer switch as specified in claim 1 wherein said current-carrying contact bridges have contact surfaces which are substantially circular in cross-section and arranged in coaxial relation to said radially outer pin of one of said plurality of contact-operating link means affixed to one of said currentcarrying contact bridges.

3. A transfer switch as specified in claim 1 wherein said radially inner pivot pin of said contact operating link means of said current-carryin contact brid es is su rted b said drive shaft in fixed r adial spacing ffom the aii s of sai drive shaft, and wherein said radially inner pivot pin of said contactoperating link means of said main contact bridges and of said auxiliary contact bridges is supported by said drive shaft in such a way as to allow the radial spacing thereof from said drive shaft to vary subject to the action of biasing spring means.

4. A transfer switch as specified in claim 1 wherein said radially inner pivot pin of each of said contact-operating link means of said current-carrying contact bridges has a radial spacing from the axis of said drive shaft exceeding the radial spacing of said radially inner pivot pin of each of said contactoperating link means of said main contact bridges and of said auxiliary contact bridges.

5. A transfer switch as specified in claim 1 wherein said drive shaft includes a contact-operating member defining a bearing arranged relatively remote from the axis of said drive shaft for said radially inner pivot pin of said contact-operating link means of said current-carrying contact bridges,and wherein said drive shaft includes an additional contact-operating member defining a radially extending slot relatively close. to the axis of said drive shaft receiving said radially inner pivot pin of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges and further receiving a helical biasing spring biasing said radially inner pivot pin of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges away from the axis of said drive shaft.

16. A transfer switch for tap-changing regulating transformer including a plurality of pairs of fixed spaced contacts arranged in a sector of a circle pattern, said plurality of pairs of fixed contacts including pairs of fixed main contacts, pairs of fixed auxiliary contacts arranged between said pairs of fixed main contacts, and pairs of fixed current-carrying contacts each arranged adjacent to one pair of said pairs of fixed main contacts on the side thereof opposite to one pair of said pairs of fixed auxiliary contacts;

. a plurality of movable main contact bridges and movable auxiliary contact bridges each arranged to selectively engage one pair of said pairs of fixed main contacts or one pair of said pairs of fixed auxiliary contacts and each pivotally connected to one pair of pairs of spaced contact-operating links;

c. a pivotable drive shaft arranged in the center of said sector of a circle pattern at right angles to the planes defined by said said plurality of pairs of fixed contacts;

. a pair of joint pivot means on the end of each of said pairs of contact-operating links of each of said plurality of main contact bridges and auxiliary contact bridges remote from main contact bridges and said auxiliary contact bridges operated by said drive shaft by the intermediary of a pair of lost motion connections each having a radially outer end and each being interposed between said drive shaft and said pair of joint pivot means;

e. a pair of movable current-carrying contact bridges each cooperating with one pair of said pairs of fixed currentcarrying contacts, each hingedly supported by one of said main contact bridges, and each pivotally connected to a pair of contact-operating links; and

f. pivot means on one end of said pair of contact-operating links of each said pair of current-carrying contact bridges operated by said drive shaft, said pivot means being connected to said drive shaft at a point spaced farther away from the axis of said drive shaft than said radially outer end of said pair of lost motion connections. 

1. A transfer switch for tap-changing regulating transformers including a. a substantially cylindrical contact support of insulating material; b. a plurality of pairs of fixed contacts supported by said contact support and arranged in a circular pattern, the constituent contacts of each of said plurality of pairs of contacts being spaced in a direction longitudinally of the axis of said contact support, said plurality of pairs of fixed contacts including pairs of fixed main contacts, pairs of fixed auxiliary contacts arranged between said pairs of fixed main contacts, and pairs of fixed current-carrying contacts each arranged adjacent one of said pairs of fixed main contacts on the side thereof opposite to one pair of said pairs of fixed auxiliary contacts; c. a plurality of movable contact bridges each arrangeD to selectively engage one of said plurality of pairs of fixed contacts and to be separated from said one of said plurality of pairs of fixed contacts, said plurality of contact bridges including main contact bridges each arranged to cooperate with one pair of said pairs of fixed main contacts, auxiliary contact bridges each arranged to cooperate with one pair of said pairs of fixed auxiliary contacts, and current-carrying contact bridges each arranged to cooperate with one pair of said pairs of fixed current-carrying contacts, each of said current-carrying contact bridges having a pair of lateral projections spaced in a direction longitudinally of said axis of said contact support and extending toward one of said main contact bridges immediately adjacent thereto; d. a drive shaft selectively pivotable in opposite directions for operating said plurality of contact bridges arranged along the axis of said contact support; and e. a plurality of contact-operating link means each having a radially inner pivot pin jointly pivotable with said drive shaft and a radially outer pivot pin affixed to one of said plurality of contact bridges, and said radially outer pivot pin affixed to each of said main contact bridges projecting through said pair of lateral projections of one of said currentcarrying contact bridges and hingedly supporting said one of said current-carrying contact bridges on said one of said main contact bridges.
 2. A transfer switch as specified in claim 1 wherein said current-carrying contact bridges have contact surfaces which are substantially circular in cross-section and arranged in coaxial relation to said radially outer pin of one of said plurality of contact-operating link means affixed to one of said current-carrying contact bridges.
 3. A transfer switch as specified in claim 1 wherein said radially inner pivot pin of said contact operating link means of said current-carrying contact bridges is supported by said drive shaft in fixed radial spacing from the axis of said drive shaft, and wherein said radially inner pivot pin of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges is supported by said drive shaft in such a way as to allow the radial spacing thereof from said drive shaft to vary subject to the action of biasing spring means.
 4. A transfer switch as specified in claim 1 wherein said radially inner pivot pin of each of said contact-operating link means of said current-carrying contact bridges has a radial spacing from the axis of said drive shaft exceeding the radial spacing of said radially inner pivot pin of each of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges.
 5. A transfer switch as specified in claim 1 wherein said drive shaft includes a contact-operating member defining a bearing arranged relatively remote from the axis of said drive shaft for said radially inner pivot pin of said contact-operating link means of said current-carrying contact bridges,and wherein said drive shaft includes an additional contact-operating member defining a radially extending slot relatively close to the axis of said drive shaft receiving said radially inner pivot pin of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges and further receiving a helical biasing spring biasing said radially inner pivot pin of said contact-operating link means of said main contact bridges and of said auxiliary contact bridges away from the axis of said drive shaft.
 6. A transfer switch for tap-changing regulating transformer including a plurality of pairs of fixed spaced contacts arranged in a sector of a circle pattern, said plurality of pairs of fixed contacts including pairs of fixed main contacts, pairs of fixed auxiliary contacts arranged between said pairs of fixed main contacts, and pairs of fixed current-carrying contacts each arranged adjacent to one pair of said pairs of fixed main contacts oN the side thereof opposite to one pair of said pairs of fixed auxiliary contacts; b. a plurality of movable main contact bridges and movable auxiliary contact bridges each arranged to selectively engage one pair of said pairs of fixed main contacts or one pair of said pairs of fixed auxiliary contacts and each pivotally connected to one pair of pairs of spaced contact-operating links; c. a pivotable drive shaft arranged in the center of said sector of a circle pattern at right angles to the planes defined by said said plurality of pairs of fixed contacts; d. a pair of joint pivot means on the end of each of said pairs of contact-operating links of each of said plurality of main contact bridges and auxiliary contact bridges remote from main contact bridges and said auxiliary contact bridges operated by said drive shaft by the intermediary of a pair of lost motion connections each having a radially outer end and each being interposed between said drive shaft and said pair of joint pivot means; e. a pair of movable current-carrying contact bridges each cooperating with one pair of said pairs of fixed current-carrying contacts, each hingedly supported by one of said main contact bridges, and each pivotally connected to a pair of contact-operating links; and f. pivot means on one end of said pair of contact-operating links of each said pair of current-carrying contact bridges operated by said drive shaft, said pivot means being connected to said drive shaft at a point spaced farther away from the axis of said drive shaft than said radially outer end of said pair of lost motion connections. 